I've fixed, mainly via text edit, some old levels to current tile namings.
Jumpers from
Lix tutorial levels by geoo
16 x 16 by Akseli from the Lix Double-Level Contest 2014
Planet Dulux by Akseli from the Lix Double-Level Contest 2014
Palmtree Pile-up (V1.2) by Simon from the Level Design Contest 5
These levels should show no missing terrain anymore but I can't guarantee their solvability or that they haven't gotten pointless.
All levels should be solvable (Lix 0.9.13).
Edit: There are fixes that remove the gaps to Planet Dulux and 16x16 (both by Akseli) in
this post.